/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/ShapeFunctions.h
Get the input Box expanded by adding the ExpandBy parameter to both the Min and Max. Dimensions will be clamped to the center point if any of ExpandBy are larger than half the box size
static FBox GetExpandedBox ( FBox Box, FVector ExpandBy )